1. Field of the Invention
The present invention relates to a structure of vehicle seat with a lifter for causing vertical displacement of the seat, in which a linkage of the lifter is provided to at least a forward portion of a seat back of the seat. In particular, the invention is directed to a vehicle seat structure of this kind wherein a forward slippage preventive element is provided to the lifter linkage so as to prevent a passenger from slipping and being slid forwardly on the seat when a collision or the like occurs.
2. Description of Prior Art
In the case of an abrupt deceleration or stop of a vehicle, a passenger on a seat in the vehicle is naturally caused to displace forwardly under the influence of inertia. Such forward displacement of passenger is basically prevented by a seat belt which restrains the passenger to the seat. However, in such an emergency case as a collision, the stop of the vehicle is so abrupt that, in spite of the restraint by seat belt, the buttocks portion of the passenger is forcibly slipped or slid forwardly on a seat cushion of the seat and sunk into the upper elastic portion of the seat cushion, with a high likelihood that the lower body portion of the passenger will be damaged or injured. This is what is called “forward buttocks slippage phenomenon”.
Hitherto, various attempts have been made to prevent such forward buttocks slippage phenomenon. For example, the Japanese Laid-Open Patent Publication No. 2002-46513 discloses a cross rod member provided in the seat cushion, the cross rod member extending transversely of the forward region of the seat cushion to thereby prevent forward slippage of the passenger's buttocks portion on the seat cushion. Namely, in the case of sudden collision, the passenger's buttocks portion, which is being slipped and sunk into the seat cushion, is quickly contacted with the cross rod member and thus prevented against further forward movement, thereby protecting the lower body portion of passenger.
Incidentally, among the vehicle seats, there has been known a vehicle seat having a seat lifter provided therein, as disclosed for example from the Japanese Laid-Open Patent Publication No. 2001-88589. According thereto, the seat lifter has a pair of links pivotally connected with the respective right and left lateral sides of the seat cushion, and operation of the seat lifter causes vertical movement of the forward end portion of seat cushion.
It may be possible to connect the aforementioned cross rod member taught in the Pub. No. 2002-46513 between the pair of links of the seat lifter associated with the Pub. No. 2001-88589 in order to prevent the above-stated forward buttocks slippage problem. However, in that case, when a sudden collision occurs and the passenger's buttocks portion is about to slip on the seat cushion as discussed above, it is more likely than not that a large load applied from the passenger's buttocks portion to the cross rod member will deform both of the two links of the seat lifter. Namely, both two links will be twisted in either the right or left directions or bent in a direction laterally of the seat cushion. Of course, to solve such problem, one can contemplate increasing the thickness of the links to resist such large load. But, it will require reinforcing the pivot points and peripheral elements associated with the links, which will result in an undesired complicated structure and increase of its size.